U.S. patent application number 09/882991 was filed with the patent office on 2001-11-01 for cube corner geometric structures in a substrate formed by both replicating and machining processes.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Benson, Gerald M., Smith, Kenneth L..
Application Number | 20010036533 09/882991 |
Document ID | / |
Family ID | 26837223 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010036533 |
Kind Code |
A1 |
Smith, Kenneth L. ; et
al. |
November 1, 2001 |
Cube corner geometric structures in a substrate formed by both
replicating and machining processes
Abstract
A cube corner article having a structured surface of geometric
structures, each geometric structure having a plurality of faces at
least some of which are arranged as a cube corner element, is made
by providing a first substrate having a plurality of grooves
therein, replicating the first substrate in a second substrate, and
forming a second plurality of grooves in the second substrate.
Geometric structures in the second substrate are formed in part by
replication of the first plurality of grooves and in part by the
formation of the second plurality of grooves.
Inventors: |
Smith, Kenneth L.; (White
Bear Lake, MN) ; Benson, Gerald M.; (Woodbury,
MN) |
Correspondence
Address: |
Office of Intellectual Property Counsel
3M Innovative Properties Company
PO Box 33427
St. Paul
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
26837223 |
Appl. No.: |
09/882991 |
Filed: |
June 15, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09882991 |
Jun 15, 2001 |
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09474913 |
Dec 28, 1999 |
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6277470 |
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09474913 |
Dec 28, 1999 |
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09075690 |
May 11, 1998 |
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6136416 |
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09075690 |
May 11, 1998 |
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08726333 |
Oct 3, 1996 |
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5759468 |
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08726333 |
Oct 3, 1996 |
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08326587 |
Oct 20, 1994 |
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08326587 |
Oct 20, 1994 |
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08139448 |
Oct 20, 1993 |
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Current U.S.
Class: |
428/167 ;
428/172; 428/338 |
Current CPC
Class: |
Y10T 29/49813 20150115;
Y10T 428/24521 20150115; Y10T 428/24752 20150115; Y10T 428/2457
20150115; Y10T 428/268 20150115; Y10T 428/24479 20150115; Y10T
428/24653 20150115; Y10T 428/31 20150115; Y10T 428/24628 20150115;
Y10T 29/49787 20150115; Y10T 428/24669 20150115; Y10T 428/24587
20150115; Y10T 428/24488 20150115; Y10T 29/49861 20150115; Y10T
428/24612 20150115; Y10T 428/30 20150115; G02B 5/124 20130101 |
Class at
Publication: |
428/167 ;
428/172; 428/338 |
International
Class: |
B32B 003/28; B32B
003/30; B32B 003/00 |
Claims
What is claimed is:
1. A unitary substrate having a plurality of faces therein defining
a plurality of geometric structures, at least some of which
comprise cube corner faces that are approximately mutually
perpendicular, at least some of the cube corner faces being formed
by replication and at least other of the cube corner faces being
formed by direct machining.
2. The substrate of claim 1, wherein at least some of the geometric
structures have at least one cube corner face formed by replication
and at least another cube corner face formed by direct
machining.
3. The substrate of claim 1, wherein at least some of the geometric
structures have substantially all of the cube corner faces formed
by direct machining.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application of pending prior
application Ser. No. 09/474,913, filed on Dec. 28, 1999, which is a
continuation application of prior application Ser. No. 09/075,690,
(issued Oct. 24, 2000, as U.S. Pat. No. 6,136,416), filed on May
11, 1998, which is a continuation application of prior application
Ser. No. 08/726,333 (issued Jun. 2, 1998, as U.S. Pat. No.
5,759,468A), filed on Oct. 3, 1996, which is a file wrapper
continuation of U.S. patent Ser. No. 08/326,587 filed Oct. 20,
1994, now abandoned, which is a continuation-in-part of U.S. patent
Ser. No. 08/139,448, filed Oct. 20, 1993, now abandoned.
FIELD OF THE INVENTION
[0002] This invention relates to retroreflective articles having
prismatic retroreflective elements.
BACKGROUND
[0003] Many types of retroreflective articles are known, and are
made in a variety of ways. One common type of retroreflective
article uses transparent microspheres, typically with hemispheric
retroreflectors thereon. Examples of this type of retroreflector
are disclosed in U.S. Pat. No. 2,407,680 (Palmquist), U.S. Pat. No.
3,190,178 (McKenzie), and U.S. Pat. No. 4,025,159 (McGrath).
[0004] Another type of retroreflective article includes prismatic
designs incorporating one or more structures commonly known as cube
corners. Retroreflective sheeting which employs cube corner type
reflective elements is well known. An example of such designs is
shown in U.S. Pat. No. 3,684,348 (Rowland).
[0005] The manufacture of retroreflective cube corner element
arrays is accomplished using molds made by different techniques,
including those known as pin bundling and direct machining. Molds
manufactured using pin bundling are made by assembling together
individual pins which each have an end portion shaped with features
of a cube corner retroreflective element. For example, certain pin
bundled arrays permit elaborate assembly into various pin
structural configurations. U.S. Pat. No. 3,926,402 (Heenan et al)
and U.S. Pat. No. 3,632,695 (Howell) are examples of pin
bundling.
[0006] The direct machining technique, also known generally as
ruling, comprises cutting portions of a substrate to create a
pattern of grooves which intersect to form cube corner elements.
The grooved substrate is referred to as a master mold from which a
series of impressions, i.e. replicas, may be formed. In some
instances, the master is useful as a retroreflective article,
however replicas, including multi-generational replicas, are more
commonly used as the retroreflective article. Direct machining is
an excellent method for manufacturing master molds for small
micro-cube arrays. Small microcube arrays are particularly
beneficial for producing thin replica arrays with improved
flexibility, such as continuous rolled goods for sheeting purposes.
Micro-cube arrays are also more conducive to continuous process
manufacturing. The process of manufacturing large arrays is also
relatively easier using direct machining methods rather than other
techniques. One example of direct machining is shown in U.S. Pat.
No. 4,588,258 (Hoopman).
SUMMARY OF INVENTION
[0007] The invention, in one broad aspect, comprises forming
geometric structures in a substrate by processing a first substrate
having a first plurality of grooves therein. A replica of the first
substrate is made in a second substrate. Then, a second plurality
of grooves are formed in the second substrate. The replication
process can comprise one or more individual replication procedures,
and the second substrate can comprise a positive or negative copy
of the first substrate. Geometric structures in the final substrate
are formed in part by replication of the first plurality of grooves
and in part by the formation of the second plurality of
grooves.
[0008] The invention relates generally to a method of manufacturing
a cube corner article comprising the steps of providing an initial
non-unitary cube corner element array comprising a plurality of
geometric structures including cube corner elements, producing a
replica of the cube corner element array as a substrate suitable
for forming retroreflective surfaces, and then removing part of the
substrate material comprising the replica to form at least one
cavity bounded by side walls in the replica at a depth at least
that of the cube corner elements. The replica is then replicated to
produce an additional directly machinable substrate suitable for
forming retroreflective surfaces, the substrate comprising at least
one raised section having side walls at a height at least that of
the cube corner elements. Then at least one raised section is
directly machined to form a raised zone comprising a plurality of
geometric structures including cube corner elements bounded by at
least two sets of parallel grooves.
[0009] The invention comprises a method of manufacturing a cube
corner article comprising the steps of providing an initial
directly machinable substrate formed as an initial non-unitary cube
corner element array comprising a plurality of geometric structures
including cube corner elements, and removing part of the substrate
material comprising the array to form at least one cavity bounded
by side walls in the substrate at a depth at least equal to the
height of the cube corner elements. The initial substrate is then
replicated to produce an additional directly machinable substrate
suitable for forming retroreflective surfaces, with the additional
directly machinable substrate comprising at least one raised
section having side walls at a height at least that of the cube
corner elements. At least one raised section is then directly
machined to form a zone comprising a plurality of geometric
structures including cube corner elements bounded by at least two
sets of parallel grooves.
[0010] The invention relates generally to a cube corner article
which is a machined replica of a non-unitary initial array
comprising geometric structures including cube corner elements. The
article has at least one directly machined raised zone of geometric
structures including cube corner elements.
BRIEF DESCRIPTION OF DRAWING
[0011] FIG. 1 is a plan view of a conventional pin bundled full
cube corner element array master for manufacturing retroreflective
sheeting.
[0012] FIG. 2 is a section view taken along line 2-2 of FIG. 1.
[0013] FIG. 3 is a plan view of a conventional pin bundled directly
machined cube corner element array master for manufacturing
retroreflective sheeting.
[0014] FIG. 4 is a section view taken along lines 4-4 of FIG.
3.
[0015] FIG. 5 is a plan view of a retroreflective replica of the
master shown in FIG. 3.
[0016] FIG. 6 is a section view taken along lines 6-6 of FIG.
5.
[0017] FIG. 7 is a plan view of a directly machinable substrate
comprising a cavity portion formed in parallel alignment with one
of the groove sets formed, in the substrate.
[0018] FIG. 8 is a section view taken along lines 8-8 of FIG.
7.
[0019] FIG. 9 is a plan view of an additional directly machinable
substrate formed by replicating the substrate shown in FIG. 7.
[0020] FIG. 10 is a section view taken along lines 10-10 of FIG.
9.
[0021] FIG. 11 is a plan view of a directly machined substrate in
which a plurality of zones of geometric structures included cube
corner elements is shown.
[0022] FIG. 12 is a section view taken along lines 12-12 of FIG.
11.
[0023] FIG. 13 is a plan view of a directly machined substrate
comprising a plurality of zones of geometric structures and
intersecting raised zones.
[0024] FIG. 14 is a section view taken along lines 14-14 of FIG.
13.
[0025] FIG. 15 is a plan view of a directly machined cube corner
article which is a replica of a zoned substrate formed by directly
machining a series of substrates.
[0026] FIG. 16 is a section view taken along lines 16-16 of FIG.
15.
[0027] FIG. 17 is a plan view of a directly machined cube corner
article comprising a plurality of zones of retroreflective cube
corner elements having diverse cube geometry and orientation,
including one raised zone.
[0028] FIG. 18 is a section view taken along lines 18-18 of FIG.
17.
[0029] FIG. 19 is a plan view of a directly machined cube corner
article comprising a plurality of zones of retroreflective elements
having different geometries, including at least one raised
zone.
[0030] FIG. 20 is a section view taken along lines 20-20 of FIG.
19.
[0031] FIG. 21 is a plan view of a directly machined cube corner
article comprising a plurality of zones of geometric structures
including retroreflective cube corner elements, including one zone
comprising cube corner elements having heights greater than cube
corner elements in adjacent zones.
[0032] FIG. 22 is a section view taken along lines 22-22 of FIG.
21.
[0033] FIG. 23 is a plan view of a directly machined cube corner
article comprising a plurality of retroreflective cube corner
elements and one raised section.
[0034] FIG. 24 is a section view taken along lines 24-24 of FIG.
23.
[0035] FIG. 25 is a plan view of a directly machined cube corner
article comprising a plurality of zones of geometric structures
including retroreflective cube corner elements, and one raised zone
not bounded by grooves in a groove set.
[0036] FIG. 26 is a section view taken along lines 26-26 of FIG.
25.
[0037] FIG. 27 is a plan view of a directly machined cube corner
article comprising a plurality of zones of geometric structures
including retroreflective cube corner elements, and a plurality of
multiple noninterfering raised zones.
[0038] FIG. 28 is a section view taken along lines 28-28 of FIG.
27.
[0039] FIG. 29 is a section view taken along lines 29-29 of FIG.
27.
[0040] FIG. 30 is a plan view of an initial pin bundled directly
machinable substrate in which a plurality of geometric structures
have been formed by directly machining one set of parallel grooves
in the substrate.
[0041] FIG. 31 is a section view taken along lines 31-31 of FIG.
30.
[0042] FIG. 32 is a section view taken along lines 32-32 of FIG.
30.
[0043] FIG. 33 is a plan view of a replica of the substrate of FIG.
30.
[0044] FIG. 34 is a section view taken along lines 34-34 of FIG.
33.
[0045] FIG. 35 is a section view taken along lines 35-35 of FIG.
33.
[0046] FIG. 36 is a plan view of the replica article shown in FIG.
33, comprising additional grooves formed in raised sections within
the orientation of the initial groove set.
[0047] FIG. 37 is a section view taken along lines 37-37 of FIG.
36.
[0048] FIG. 38 is a section view taken along lines 38-38 of FIG.
36.
[0049] FIG. 39 is a plan view of a directly machined two groove set
cube corner article comprising a plurality of zones of
retroreflective cube corner elements.
[0050] FIG. 40 is a section view taken along lines 40-40 of FIG.
39.
[0051] FIG. 41 is a section view taken along lines 41-41 of FIG.
39.
[0052] FIG. 42 is a plan view of a pin bundled full cube array with
a directly machined cavity.
[0053] FIG. 43 is a section view taken along line 43-43 of FIG.
42.
[0054] FIG. 44 is a plan view of a cube corner article formed as a
machined replica of the array shown in FIG. 42.
[0055] FIG. 45 is a section view taken along line 45-45 of FIG.
44.
[0056] FIG. 46 is a section view of a cube corner article having a
plurality of zones of geometric structures including raised zones
and cube corner elements which form boundary edges of separation
surfaces.
[0057] FIG. 47 is a section view of a cube corner article
comprising a plurality of zones of geometric structures including
raised zones suitable for holding a sealing medium above geometric
structures in at lease one other zone.
[0058] FIG. 48 is a section view of a cube corner article
comprising a plurality of raised zones and including a plurality of
raised sections suitable for holding a sealing medium above zones
comprising retroreflective surfaces of geometric structures.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0059] The manufacture of retroreflective cube corner element
arrays is accomplished using either unitary or non-unitary, i.e.
assembled, molds made by different techniques. These techniques
include, inter alia, those known as pin bundling and direct
machining. Assembled molds manufactured using pin bundling, such as
initial non-unitary master mold 2 shown in FIG. 1 and FIG. 2, are
made by assembling together zones 4 of individual pins which each
have an end portion shaped with features of a cube corner
retroreflective element, as shown by full cube corner elements 6,
8. Certain pin bundled arrays permit elaborate assembly into
various pin structural configurations. U.S. Pat. No. 3,926,402
(Heenan et al), is one example of pin bundling.
[0060] Direct machining is often a preferred method for efficiently
manufacturing master molds for small microcube arrays. This is due
to the advantages derived from directly machined substrates in the
production of thin replica arrays with improved flexibility, and
the often relatively more efficient manufacturing steps when
compared with pin bundling. An example of a direct machined
substrate is taught in U.S. Pat. No. 3,712,706 (Stamm). The Stamm
patent and U.S. Pat. No. 4,588,258 (Hoopman) are each examples of
structures formed by single or multiple passes of a machine tool
having two opposing cutting surfaces for cutting grooves to form
cube corner optical faces in a substrate.
[0061] It is recognized that directly machined grooves are
preferably machined as groove sets comprising a plurality of
separate and parallel grooves. In the direct machining patent
examples cited above, at least three groove sets are required.
However, examples of direct machining involving only two sets of
grooves are shown in U.S. Pat. No. 4,349,598 (White) and U.S. Pat.
No. 4,895,428 (Nelson et al).
[0062] Retroreflective cube corner element arrays are typically
derived from matched pairs of cube corner retroreflecting elements,
i.e. cubes which are geometrically congruent and rotated
180.degree., such as cube corner element 12 and cube corner element
14 shown in directly machined pin bundled cube corner article 16 of
FIG. 3, which is similar to the non-unitary substrate shown in U.S.
Pat. No. 4,243,618 (Van Arnam). The cube corner elements in article
16 are bounded by grooves having identical groove depths, and are
the same element length. The highest points in conventional three
groove arrays are defined by the cube peaks 20. All of the elements
in article 16 are the same height above a common reference plane
18, as shown in FIG. 4. Other examples of this fundamental matched
pair concept relating to conventional cube arrays is shown in U.S.
Pat. No. 3,712,706 (Stamm), U.S. Pat. No. 4,588,258 (Hoopman), U.S.
Pat. No. 1,591,572 (Stimson), U.S. Pat. No. 2,310,790 (Jungerson),
and U.S. Pat. No. 5,122,902 (Benson), and German patent reference
DE 42 42 264 (Gubela).
[0063] Referring again to FIG. 3 and FIG. 4, one example of
conventional non-canted cube corner elements is shown having three
sides when viewed in plan view, and having an equilateral triangle
formed at the base of each cube corner reflecting element. These
cube corner reflecting elements are formed by three groove sets
directly machined into a substrate. FIG. 3 shows a plan view of a
directly machined cube corner article useful as a non-unitary
master mold which is then replicated, or plated, to form a unitary
cube corner article 22 as shown in FIG. 5 and FIG. 6. Referring
again to FIG. 3, the grooves 25 in non-parallel groove sets
mutually intersect at representative locations 27.
[0064] FIGS. 3 and 4 disclose cube corner element retroreflective
arrays comprising non-canted cubes which have individual symmetry
axes 19 that are perpendicular to a plane 18. The symmetry axis is
a central or optical axis which is a trisector of the internal or
dihedral angles defined by the faces of the element. However, in
some practical applications it is advantageous to cant or tilt the
symmetry axes of the matched pair of cube corner retroreflective
elements to an orientation which is not perpendicular to the base
plane. The resulting canted cube-corner elements combine to produce
an array which retroreflects over a wide range of entrance angles.
This is taught in U.S. Pat. No. 4,588,258 (Hoopman), and is later
shown below in relation to other figures. Canting may be in either
a forward or backward direction. The Hoopman patent includes
disclosure of a structure having an amount of cant up to 13.degree.
for a refractive index of 1.5. Hoopman also discloses a cube with a
cant of 9.736.degree.. This geometry represents the maximum forward
cant of cubes in a conventional directly machined array before the
grooving tool damages cube optical surfaces. The damage normally
occurs during formation of a third groove when the tool removes
edge portions of adjacent elements. U.S. Pat. No. 2,310,790
(Jungerson) discloses a structure which is canted in a direction
opposite that shown in the Hoopman patent.
[0065] For these conventional arrays, optical performance is
conveniently defined by the percent of the surface area that is
actually retroreflective, i.e. which comprises an effective area of
active aperture. The percent active aperture varies as a function
of the amount of canting, refractive index, and the entrance
angle.
[0066] At non-zero entrance angles, conventional directly machined
arrays display, at most, two different aperture shapes of roughly
similar size. These result from the single type of geometrically
congruent matched pairs of conventional cube corner elements.
Canted conventional cube corner arrays exhibit similar trends,
although the shape of the aperture is affected by the degree of
canting.
[0067] Some conventional cube corner arrays are manufactured with
additional optical limitations, perhaps resulting from canting or
other design features, to provide very specific performance under
certain circumstances One example of this is the structure
disclosed in U.S. Pat. No. 4,895,428 (Nelson et al), and which is
shown in a multiple zone modified configuration in several figures
below. In these geometries, the cube corner elements are each
canted in a backward direction to the point that each of the base
triangles is eliminated.
[0068] Referring again to conventional arrays, U.S. Pat. No.
4,202,600 (Burke et al), and U.S. Pat. No. 4,243,618 (Van Arnam)
disclose, and incorporate by reference, the triangular based cube
corner reflecting elements or prisms shown in Stamm. The Burke et
al. patent discloses tiling of these prisms in multiple differently
oriented zones to produce an appearance of uniform brightness to
the eye when viewed at a high angle of incidence from at least a
minimum expected viewing distance. The Van Arnam reference
discloses use of pin bundling to create disoriented patterns of
cube corner trigonal pyramids and cutting a grid of grooves into a
mold formed by the bundled pins. In this manner, the pins may be
cut so that sheeting formed from the molds contains raised grids
for bonding a backing material to the sheeting.
[0069] Some pin bundled retroreflective articles also comprise a
grid or ridge-like structure, such as the examples shown in U.S.
Pat. No. 4,243,618 (Van Arnam), U.S. Pat. No. 4,202,600 (Burke et
al), U.S. Pat. No. 4,726,706 (Attar), U.S. Pat. No. 4,208,090
(Heenan), U.S. Pat. No. 4,498,733 (Flanagan), U.S. Pat. No.
3,922,065 (Schultz), U.S. Pat. No. 3,417,959 (Schultz), and U.S.
Pat. No. 3,924,929 (Holmen). Another ridge-like structure in a
retroreflective article is taught, primarily, for a microsphere or
beaded sheeting construction, in U.S. Pat. No. 4,025,159 to
McGrath. Ridge-like structures are utilized in these examples to
provide raised grids for bonding a backing material to the
sheeting. Another example of ridge-like structures in pin bundled
retroreflective articles is shown within U.S. Pat. No. 3,632,695
(Howell), in which each ridgelike structure is shaped as a lens
area to transmit, rather than reflect, light from a source.
[0070] The invention comprises retroreflective cube corner articles
and sheetings, and methods of manufacture, which substantially
advance the state of the art of cube corner elements. This results
from use of novel manufacturing processes, and directly machined
cube corner article designs which greatly enhance the
retroreflective performance and produce arrays having novel raised
zones.
[0071] FIG. 7 is a plan view and FIG. 8 is a section view of a
replica 70 of a directly machinable substrate having geometric
patterns which are similar, in part, to the patterns shown in
sheeting 22 shown in FIG. 5. In this embodiment, replica 70
comprises zone 73 having a plurality of geometric structures
including identical cube corner elements, such as individual
elements 75. Part of the substrate material is removed to form at
least one cavity 77 bounded by a base 78 and side walls 79 in the
substrate, as shown in the section view of FIG. 10. Side walls 79
are machined to a depth D' which is at least that of the depth D"
of the initial sets of parallel grooves. In addition to using the
preferred substrate materials discussed below, it must be possible
to separate replicas from the original pattern or substrate. In
some cases, this requires the use of a parting layer between the
original and the replica substrates. The parting layer permits
separation of replicas by preventing adhesion between the materials
of the original and replica materials. Parting layers may consist
of a variety of materials such as an induced surface oxidation
layer, an intermediate thin metallic coating, chemical silvering,
or combinations of different materials and coatings.
[0072] An additional unitary substrate is then formed as a replica
80, as shown in FIG. 9, of directly machinable replica 70.
Selection of an appropriate additional unitary substrate must take
into account the requirements of replication accuracy of features
in the initial substrate, the suitability of the additional unitary
substrate for formation of geometric structures including
retroreflective cube corner elements, and the ability to separate
the additional substrate from the initial substrate without damage
to any geometric feature. A non-unitary initial substrate, a
unitary replica 70, or a unitary replica 80 is each preferably
formed of material suitable for creating retroreflective surfaces
in this embodiment. A substrate suitable for forming
retroreflective surfaces according to this invention may comprise
any material suitable for forming directly machined grooves or
groove sets. Suitable materials should machine cleanly without burr
formation, exhibit low ductility and low graininess, and maintain
dimensional accuracy after groove formation. A variety of materials
such as machinable plastics or metals may be utilized. Suitable
plastics comprise thermoplastic or thermoset materials such as
acrylics or other materials. Suitable metals include aluminum,
brass, nickel, and copper. Preferred metals include non-ferrous
metals. Preferred machining materials should also minimize wear of
the cutting tool during formation of the grooves. As a result of
cavity 79 being formed in the replica of the initial directly
machinable substrate, unitary replica 80 comprises at least one
raised section 100 as shown in FIG. 9 and FIG. 10. Additional
grooves and/or cavities may then be directly machined into replica
80, or multi-generational unitary replicas, to form a plurality of
zones of geometric structures including cube corner elements 75
bounded by at least two sets of parallel grooves, as discussed
below.
[0073] It is recognized that while the above embodiment uses an
initial non-unitary substrate similar to that shown in FIGS. 3 and
4, the type of cube corner array shown in FIGS. 1 and 2 may also be
used as an initial non-unitary substrate. It is further recognized
that the machining techniques described below may utilize any of
the various known types of assembled non-unitary substrates
including the types described above for initial nonunitary
substrates. Non-unitary initial substrates may even comprise
geometric structures which are not cube corner elements. FIG. 7
discloses replica joining line 76 of a joining line from an initial
non-unitary substrate. Replica joining lines may or may not be
apparent in replicas of an initial nonunitary substrate according
to this invention.
[0074] FIG. 11 and FIG. 12 disclose in plan view and section view
respectively another embodiment of the invention in which an
additional directly machinable unitary substrate 140 comprises
zones of cube corner elements including zone 142 and zone 146. Zone
146 may be originally formed as a raised section which is then
directly machined using a three groove set pattern. The direct
machining of a raised section produces a raised zone, which
comprises a plurality of geometric structures including cube corner
elements bounded by at least two sets of parallel grooves. In one
embodiment, such as that shown in FIG. 12, the bottom of the
deepest groove in at least one raised zone 146 is machined to a
depth which is higher relative to a common reference plane 151 than
the highest structure in any zone which is adjacent to the raised
zone. FIG. 13 and FIG. 14 disclose in plan and section view
respectively a substrate 160 comprising a plurality of intersecting
raised zones 146, also manufactured using a three groove set
pattern.
[0075] As shown in FIGS. 11-14 for embodiments including directly
machined raised zone arrays, the groove sets in a raised zone are
preferably parallel to at least one groove set in zones, e.g.
portions of the array, adjacent to raised zones. Also, the total
width of a raised zone is preferably an integral multiple of the
distance between grooves in groove sets in zones adjacent to the
raised zone. This is achieved, in one embodiment, by creating an
initial substrate with a cavity suitable for forming a raised
section which is bounded by grooves from at least one groove set in
a first cube corner element array zone. This is particularly useful
when the cubes in adjacent zones are the same geometry but
different size, i.e. geometrically similar. This results in fewer
retroreflective elements which are damaged during the manufacturing
process and therefore considerably improves the performance of
retroreflective sheetings using this construction. In addition, the
machining of raised zones does not initially require machining the
surface of a substrate with the same high measure of flatness as
when manufacturing raised sections.
[0076] Conventional cube corner retroreflective element designs
include structural and optical limitations which are overcome by
use of these raised zone cube corner retroreflective element
structures and methods of manufacture. Use of this new class of
retroreflective cube corner element structures and manufacturing
methods permits diverse cube corner element shaping. For example,
cubes in a single array may be readily manufactured with raised
discontinuous geometric structures having different heights or
different shapes. Use of these methods and structures also permits
manufacture of cube arrays which have highly tailorable optical
performance. For example, at many entrance angles, including at
zero entrance angle, raised multiple structure arrays outperform
conventional arrays by exhibiting higher percent active apertures,
multiple active aperture shapes, or by providing improved
divergence profiles, or both. Raised multiple structure
manufacturing techniques may also produce enhanced optical
performance resulting from closely spaced intermixed cubes with
different active aperture shapes and sizes. This presents more
uniform appearances of raised multiple structure arrays over a wide
range of viewing distances under both day and night observation
conditions. These advantages of raised multiple structure cube
corner elements and zones enhance the usefulness of articles having
these features. Such articles include, for example, traffic control
materials, retroreflective vehicle markings, photoelectric sensors,
directional reflectors, flexible retroreflective arrays, and
reflective garments for human or animal use.
[0077] As discussed above, many limiting cases of conventional cube
corner element design are surpassed through use of raised multiple
structure methods of manufacture. In some raised multiple structure
designs, such as that shown in substrate 140 in FIG. 11, cube
surfaces having some conventional cube geometries may occur as part
of a plurality of cube types in a single array. However, the normal
limits of conventional cube shapes and performances are not
similarly bounded using raised multiple structure methods and
structures.
[0078] FIG. 15 and FIG. 16 are plan and section views respectively
of an alternate embodiment substrate 200, which is a machined
replica of a two groove set modified unitary substrate formed from
an initial non-unitary cube corner element array. Substrate 200
comprises a plurality of zones 206, 208 of geometrically similar
cube corner elements 212, 216. Substrate 200 includes a raised zone
208 which comprises a plurality of geometric structures including
cube corner elements 212 which are a different size and which are
at a different height above a common reference plane 214 than cube
corner elements 216 in zone 206. Substrate 200 is particularly
useful in applications requiring high brightness at high entrance
angles such as pavement markers, approach markers, channel markers,
roadway dividers, barriers, and similar uses.
[0079] FIG. 17 and FIG. 18 are plan and section views respectively
of another alternate embodiment substrate 250, which is a machined
replica of a three groove set modified unitary substrate formed
from an initial nonunitary cube corner element array. Substrate 250
comprises a plurality of zones 252, 254, including at least one
raised zone. Raised zone 254 comprises a plurality of geometric
structures including cube corner elements 260 which are a different
size and shape, and are at a different height above a common
reference plane 263, than cube corner elements 265 in zone 252.
Raised zone 254 is shown with one secondary groove set having
directly machined secondary grooves 266 in parallel relation with
grooves in an adjacent zone. In this embodiment, two of the grooves
in the adjacent zone bound raised zone 254 so that the total width
of the raised zone is an integral multiple of the distance between
the grooves in the groove set in the zone adjacent to raised zone
254. Another secondary groove set having directly machined
secondary grooves 267 is arranged in non-parallel relation with any
grooves in adjacent zones. Grooves 268 in a primary groove set are
also arranged in non-parallel relation with any grooves in adjacent
zones. It is recognized that any of the grooves may be designated
for parallel alignment with grooves in an adjacent zone, depending
on the desired orientation. This permits orientation of cube corner
elements 260 in virtually any manner to optimize optical
performance, however, this is accomplished without damage to any
structures in adjacent zone 252.
[0080] FIG. 17 further discloses a raised zone multiple structure
cube array 250 having at least one zone 254 in which primary
grooves 268 do not pass through the secondary grooves 266, 267 at
the mutual intersection locations 269 of the secondary grooves.
Primary grooves 268 are equally spaced and centered on secondary
groove intersection locations 269. Array 250 presents yet another
novel feature of raised multiple structure cube corner technology.
In particular, a method is disclosed for manufacturing a cube
corner article by directly machining three non-parallel
non-mutually intersecting sets of grooves. Preferably, these sets
intersect at included angles less than 90.degree. It is recognized
that certain machining imprecisions may create minor, unintentional
separation between grooves at intersections. However, this aspect
of the invention involves intentional and substantial
separation.
[0081] For example, a separation distance between the intersections
of the grooves within two groove sets with at least one groove in a
third groove set which is greater than about 0.01 millimeter would
likely provide the advantages of this feature. However, the precise
minimum separation distance is dependent on the specific tooling,
substrate, process controls, and the desired optical performance
sought.
[0082] Non-mutually intersecting groove sets create multiple
different geometric structures including cube corner elements with
different active aperture sizes and shapes. Entire arrays, such as
array 250, may even be formed with cube corners created by a
combination of mutually and nonmutually intersecting groove sets.
The position of the groove sets is controlled to produce maximum
total light return over a desired range of entrance angles. Also
the distance between grooves in at least one groove set might not
be equal to the distance between grooves in at least another of the
groove sets. It is also possible to machine at least one set of
parallel grooves into a substrate in a repeating fashion with the
set comprising a distance between grooves which is optionally
variable at each machining of the set. Also, a portion of any one
of the grooves may be machined to a depth that is different from at
least one other groove depth.
[0083] FIG. 19 and FIG. 20 are plan and section views respectively
of another alternate embodiment substrate 270, which is a modified
replica of a mixed two groove set and three groove set modified
unitary substrate formed from an initial non-unitary cube corner
element array. Substrate 270 comprises a plurality of zones 274,
276, including at least one raised zone. Raised zone 276 comprises
a plurality of geometric structures including cube corner elements
280, formed with three groove sets, which are a different size and
shape, and are at a different height above a common reference plane
283 than cube corner elements 285, formed with two groove sets, in
zone 274. Indeed, raised zone 276 comprises grooves which are
machined to a depth which is higher relative to common reference
plane 283 than the highest structure, e.g. cubes 285, in the
adjacent zone 274. Substrate 270 comprises cube corner elements
which are specifically tailored to provide peak light return at
high entrance angles, although other combinations are also
useful.
[0084] FIG. 21 and FIG. 22 are plan and section views respectively
of another alternate embodiment substrate 290. Substrate 290
comprises a plurality of zones 293, 295, including at least one
raised zone. Raised zone 295 comprises a plurality of identical
geometric structures including cube corner elements 297. Cube
corner elements 297 and cube corner elements 293 share a common
base reference plane 300, which aids considerably in processing the
article. Cube corner elements 297 are a different size, and have
peaks at a different height above a common reference plane 300,
than cube corner elements 303 in zone 293. Substrate 290 comprises
certain structures that are higher than others to help minimize
damage to cubes during processing and handling of the replica. FIG.
21 and FIG. 22 show spacing W between grooves in groove sets in
zones adjacent to the raised zone, and the corresponding spacing 2W
between grooves bounding the raised zone. It is desirable to use
this machining method which results in an article having at least
one raised zone with directly machined cube corner elements in
which the groove sets in a raised zone are parallel to a groove set
in at least on portion of the article adjacent to the raised zone,
and the distance between grooves in a groove set in a raised zone
is an integral multiple of the distance between grooves in groove
sets in areas in at least one portion of the article adjacent the
raised zone. This manufacturing innovation permits significant
reduction and/or elimination of damage to optical structures
adjacent to the raised zones.
[0085] Variable groove spacing within any groove set may also be
used to produce raised multiple structure cube arrays with
additional beneficial features. In such cases, the spacing of the
primary grooves within a groove set relative to the secondary
groove intersections is varied in a repeating pattern throughout
array. A wide range of aperture sizes and shapes will result in
this array, with a corresponding improvement in the uniformity of
the return energy pattern or divergence profile of the
retroreflected light due to diffraction. Proper placement of
grooves can be utilized advantageously during design to provide
optimum product performance for a given application. Another
beneficial feature includes manufacture of a raised zone having
cube corner elements which are of substantially identical shapes to
cube corner elements in portions of the array adjacent to the
raised zone, but with the raised zone cube corner elements
exhibiting different optical performance than cube corner elements
in the adjacent portions of the array.
[0086] Raised sections and raised zones may be manufactured in
different shapes using the methods of this invention, as shown in
FIG. 23 and FIG. 24, in which a six sided raised section 315 is
formed in substrate 319. Raised section 315 is surrounded by zone
322 having a plurality of cube corner elements 325. Raised section
315 is manufactured by replicating a modified replica of an initial
non-unitary substrate. Part of the substrate material in the
modified replica is removed to form at least one cavity. The cavity
is formed using any known technique, such as electrical-discharge
machining, photo-etching, or other precision techniques. The cavity
is bounded by side walls in the replica at a depth at least that of
the cube corner elements formed by the groove sets in adjacent
areas. The replica is then replicated to produce a cube corner
article comprising a zone 322 and at least one raised section 315
having side walls at a height at least that of the height of cube
corner elements formed in the adjacent zone.
[0087] FIG. 25 and FIG. 26 disclose a raised zone article similar
to the raised section article shown in FIG. 23 and FIG. 24, but
with a raised zone shape which is not bounded by a groove in a
groove set. Substrate 330 comprises a raised zone 333 having a
plurality of geometric structures including cube corner elements
335. The raised zone is surrounded by adjacent zone 338 having a
plurality of cube corner elements 340. In the embodiment of FIGS.
25-26, cube corner elements 335, 340 are geometrically similar. It
is recognized, however, that cube corner elements in the zones may
have diverse geometries and orientations to control optical
performance characteristics and may be positioned at different
heights relative to common reference plane 341. The invention
permits numerous combinations of structures previously unknown and
not possible within the art of retroreflective cube corner element
design and manufacturing technologies.
[0088] FIGS. 27-29 disclose views of substrate 350 in which there
is formed a plurality of both different and repeating patterns of
geometric structures including cube corner elements in multiple
independent discontinuous raised zones 352, 354. A portion of a
zone may be separated from another portion of the zone by other
structures such as a raised section or a raised zone. All portions
of a zone should be manufactured at the same time and must not
interfere with the machining of any other raised structure. This
multiple independent zone capability effectively reduces the number
of replication cycles necessary to produce arrays having greater
than two zones. The raised zones are bordered by an adjacent zone
365 having a plurality of cube corner elements 370.
[0089] FIGS. 30-32 disclose an initial pin bundled non-unitary
substrate 390, comprising a plurality of pins 400, in which one
initial groove set 398 is machined in initial raised areas 395.
Substrate 390 may either have initial recessed areas 393 or it may
require forming these areas after machining groove set 398. FIGS.
33-35 disclose views of a replica 402 of machined substrate 390. In
replica 402, the features of substrate 390 are inverted so that the
grooves formed by groove set 398 are now peaks in a zone 406, which
is lower than adjacent zone 410.
[0090] FIGS. 36-38 disclose substrate 402 which is further machined
with additional grooves 417 to produce a plurality of machined
raised sections 415. Machined raised sections 415 each have
structures which share a base plane 421 which is higher than the
base plane 424 of the similar structures in adjacent zones. Also,
the peak height of structures in adjacent zones is the same. This
is also shown in FIG. 40. FIGS. 39-41 each disclose substrate 402
which is further machined with an additional groove set comprising
a plurality of grooves 427 to form zones of cube corner elements.
Zone 436 comprises cube corner elements 438, and zone 442 comprises
cube corner elements 445. The method disclosed in FIGS. 30-41
produces the zoned cube corner articles of FIGS. 39-41 using only
one replication step.
[0091] Another embodiment of the invention comprises manufacture of
a raised zone cube corner article which also requires only one
replication step after machining an initial non-unitary substrate.
Referring to FIG. 42 and FIG. 43, initial pin bundled full cube
corner element array 447 is shown in plan and section view
respectively. Array 447 comprises a plurality of geometric
structures including cube corner elements 448. Part of the directly
machinable substrate material comprising the initial non-unitary
array is removed to form at least one cavity 449 bounded by side
walls 450 in the substrate at a depth at least equal to the height
H of the cube corner elements. Replication of the initial substrate
is then performed to produce an additional directly machinable
substrate 452, shown in FIG. 44 and FIG. 45, which is suitable for
forming retroreflective surfaces. The replica comprises at least
one raised section having side walls at a height at least that of
the cube corner elements. Direct machining using the various
techniques described above of at least one raised section then
forms a raised zone 454 comprising a plurality of geometric
structures including cube corner elements bounded by at least two
sets of parallel grooves. In this embodiment, a taper of
approximately 5.degree. is shown for ease of separation of a
replica.
[0092] FIG. 46 discloses a section view of a substrate 455,
manufactured as described above as a machined replica of a modified
unitary substrate formed from an initial non-unitary cube corner
element array. Substrate 455 comprises zones of geometric
structures including cube corner elements having different heights
and different geometries. FIG. 46 shows a plurality of geometric
structures, such as structures 459, 460, each comprising a lateral
face 461, 462 formed by a groove in a groove set. In at least one
zone, lateral faces of the geometric structures form boundary edges
46.3 of a separation surface 466. The lateral faces may include
cube corner element optical surfaces as well as non-optical
surfaces on cube corner or other geometric structures. A separation
surface 466 may have flat or curved portions when viewed in cross
section.
[0093] Other embodiments of this method include creation of an
article, or replicas of the article, which further modify the shape
of the retroreflected light pattern. These embodiments comprise,
for directly machined arrays, at least one groove side angle in at
least one set of grooves which differs from the angle necessary to
produce an orthogonal intersection with other faces of elements
defined by the groove sides. This is also stated in terms of a
sheeting having a plurality of either directly machined or pin
bundled cube corner elements each having at least one dihedral
angle which is not 90.degree. Similarly, at least one set of
directly machined grooves may comprise a repeating pattern of at
least two groove side angles that differ from one another. This
feature may also be stated in terms of a sheeting having a
plurality of either directly machined or pin bundled cube corner
elements each having, in a repeating pattern, at least one dihedral
angle which is not 90.degree.. Shapes of grooving tools, or other
techniques, may create cube corner elements in which at least a
significant portion of at least one cube corner element optical
face on at least some of the cubes are arcuate. The arcuate face
may be concave or convex. The arcuate face, which was initially
formed by one of the grooves in one of the groove sets, is flat in
a direction substantially parallel to said groove. The arcuate face
may be cylindrical, with the axis of the cylinder parallel to said
groove, or may have a varying radius of curvature in a direction
perpendicular to said groove.
[0094] Raised zone multiple structure geometries are particularly
beneficial for use in applications requiring retroreflective
sheeting having substantial total light return, such as traffic
control materials, retroreflective vehicle markings, photo-electric
sensors, signs, internally illuminated retroreflective articles,
reflective garments, and retroreflective markings. The enhanced
optical performance and design flexibility resulting from raised
zone multiple structure techniques and concepts relates directly to
improved product performance, cost efficiencies, and marketing
advantage.
[0095] Total light return for retroreflective sheeting is derived
from the product of percent active aperture and retroreflected
light ray intensity. For some combinations of cube geometries,
entrance angles, and refractive index, significant reductions in
ray intensity may result in relatively poor total light return even
though percent active aperture is relatively high. One example is
retroreflective cube corner element arrays which rely on total
internal reflection of the retroreflected light rays. Ray intensity
is substantially reduced if the critical angle for total internal
reflection is exceeded on any one of the cube faces. Metallized or
other reflective coatings on a portion of an array may be utilized
advantageously in such situations. For example, a particular raised
zone which has cube surfaces contacting a sealing medium will often
be more reflective when the surfaces have a reflective coating.
Alternately, a portion may comprise an entire array.
[0096] Separation surfaces may be advantageously utilized to
increase light transmission or transparency in sheeting, including
flexible sheeting, utilizing raised structure or multiple zone
retroreflective cube corner element arrays. For example, this is
particularly useful in internally illuminated retroreflective
articles such as signs or automotive signal light reflectors, which
are normally manufactured using injection molding.
[0097] Retroreflective directly machined cube corner articles are
often designed to receive a sealing film or backing material which
is applied to the retroreflective article in order to maintain a
low refractive index material, such as air, next to the
retroreflective elements for improved performance. In conventional
arrays this medium is often placed in direct contact with the cube
corner elements in ways which degrade total light return. However,
using raised zone multiple structure constructions, a sealing
medium may be placed on the highest surface of the array without
contacting and degrading the optical properties of lower
retroreflective cube corner elements. The highest surface may
comprise cube corner elements, non-retroreflective pyramids,
frustums, posts, or other structures. Although slight height
variations may result from slight non-uniformity of groove
positions or included angle of cube corner elements due to
machining tolerances or intentional inducement of
non-orthogonality, these variations are not analogous to the
variations disclosed and taught in this invention. For arrays using
a sealing medium, the highest surfaces may be truncated both to
hold the medium above the cube corner elements as well as to
increase the light transmissivity of the sheeting. Light
transmissivity of the sheeting may be increased through use of a
transparent or partially transparent sealing medium.
[0098] Articles manufactured according to the methods of this
invention are useful for minimizing the contact of a sealing medium
with retroreflective cube corner elements. FIG. 47 discloses one
embodiment of a substrate 470 having a plurality of zones of
geometric structures including cube corner elements. A first raised
zone comprises cubes 473 which have a height above cubes 475 in
another zone. The taller geometric structures, such as cubes 473,
provide support for a sealing medium 477 spaced above the lower
geometric structures. In similar fashion, FIG. 48 shows substrate
481 which, in addition to the geometric structures shown, in FIG.
47, also comprises raised sections 484. Raised sections 484 are
suitable for supporting sealing medium 477 above all other
geometric structures including cube corner elements 473, 475.
Raised sections 484 may also be advantageously utilized to increase
light transmission or transparency in sheeting.
[0099] Organic or inorganic transparent materials are suitable
materials for retroreflective articles or sheeting of this
invention. Preferable organic materials include polymers, including
thermoset and alkyd materials, thermoplastic materials, and certain
mixtures of polymers. Preferably, transparent materials which are
dimensionally stable, durable, weatherable, and easily replicated
into the desired configuration are used. Illustrative examples of
suitable materials include glass; acrylics, which have an index of
refraction of about 1.5, such as Plexiglas brand resin manufactured
by Rohm and Haas Company; polycarbonates, which have an index of
refraction of about 1.59; reactive materials such as taught in U.S.
Pat. Nos. 4,576,850, 4,582,885, and 4,668,558; polyethylene based
ionomers, such as those marketed under the brand name of SURLYN by
E. I. Dupont de Nemours and Co., Inc.; polyesters, polyurethanes;
and cellulose acetate butyrates. Polycarbonates are particularly
suitable because of their toughness and relatively higher
refractive index, which generally contributes to improved
retroreflective performance over a wider range of entrance angles.
These materials may also include dyes, colorants, pigments, UV
stabilizers, or other additives. Transparency of the materials
ensures that the separation or truncated surfaces will transmit
light through those portions of the article or sheeting.
[0100] The incorporation of raised sections and/or separation
surfaces does not eliminate the retroreflectivity of the article,
but rather it renders the entire article partially transparent. In
some applications requiring partially transparent materials, low
indices of refraction of the article will improve the range of
light transmitted through the article. In these applications, the
increased transmission range of acrylics (refractive index of about
1-5) is desirable.
[0101] In fully retroreflective articles, materials having high
indices of refraction are preferred. In these applications,
materials such as polycarbonates, with refractive indices of about
1.59, are used to increase the differences between the indices of
the material and air, thus increasing retroreflection.
Polycarbonates are also generally preferred for their temperature
stability and impact resistance.
[0102] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of this invention.
* * * * *